Think about how much improvement Bruce Condello and Cecil Baird have done to their BG over just a few generations of selective breeding. I suspect SMB over a hundred years in the wild could adapt some to new conditions. If you really start to look at wild fish populations, you will see huge variances in populations, even from adjacent river systems. I can often tell the difference between Potomac River RBS and Rappahannock River RBS by their coloration. They each have distinct coloration. Those rivers are within a few miles of each other but are isolated enough to show distinction. Is it enough to create a subspecies or even a strain, likely not. Natural selection is constantly working and fish are constantly evolving. I suspect if someone worked on it for a couple decades, they could breed a strain of SMB that was more adapted to pond life and could reproduce in ponds that didn't have so much rocky structure in them...